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Energy systems and 24/7 carbon free energy

Claims of “100% renewable energy” are almost always greenwashing. The electricity grid mix varies throughout the day which means most organizations claiming to use only renewable energy are doing so only on an accounting basis.

Using Renewable Energy Certificates (RECs) or Renewable Energy Guarantees of Origin (REGOs) are common, but they can’t credibly be used to back claims of 100% renewables. Power Purchase Agreements (PPAs) or green supply agreements are much more complex, but do at least deliver on the claims.

However, if the focus is on “renewables” like solar and wind, then they are still inherently variable. Even high quality products like direct PPAs can’t make up for times when there is insufficient renewable energy available on the grid.

This is why there is a push for what’s known as 24/7 carbon free energy. The goal is that every unit of consumption is generated by carbon free sources of electricity. The goal is no longer pure “renewables”, but “carbon free” or “clean”, which can include wind and solar but also allows for nuclear, hydro, long-duration storage and bio-gas.

It’s important that a broad portfolio of energy sources is considered, particularly nuclear, because the barriers are too high to achieve decarbonization goals with renewables alone.

Table comparing different options for clean energy and climate mitigation
Breakdown of options for voluntary clean energy and climate mitigation. From: Princeton University Zero Lab, 2021

Complex energy systems #

Google has been leading the drive towards the 24/7 carbon free energy goal. Amongst the three big cloud providers, Google has been a consistent leader in both pushing for 100% renewables and now 24/7 carbon free.

Microsoft has also been doing good work, but perhaps surprisingly, Google has been the most transparent. Google is aiming to match its global data center energy demand by carbon free energy 24/7 by 2030 and has published a policy roadmap towards that.

Unfortunately, it’s not just a case of building out more sources of clean energy and connecting them to the grid. Keeping the energy system in balance is tricky: grid operators must ensure that supply continually matches demand. The system has to deal with changes in weather, demand patterns from normal daily life, maintenance of equipment, and the fact that electricity is often generated nowhere near where it needs to be used.

For example, wind generates a lot of electricity in Scotland, but often needs to be curtailed because there is insufficient transmission capacity to move it down to where demand is in the South.

Graph showing hourly carbon free energy at an example data center
Graph showing the problem with variable renewables on an hourly basis at an example data center. From: Google, 2020.

System level impacts of 24/7 carbon free energy #

Google has funded two studies to look at the impact of 24/7 carbon free energy on how the grid operates. The first of these was published in 2021 for the United States and the second was recently published for Europe.

Both of these studies use open source modeling software (GenX for the US and PyPSA for Europe) to create scenarios with representative demand and a mix of generation technologies. The goal is to see how the system responds to demand and supply, and in particular to compare cost and carbon emissions vs the existing model of using 100% annual matching.

The details of the results are worth reading, but my main two takeaways1 are:

  1. Reaching 90-95% carbon free energy can be achieved with only a small cost premium compared to 100% annual matching. However, pushing closer to 100% significantly increases the cost to more than double.

  2. There is a big assumption about the available technologies, including long-duration battery/energy storage which has yet to be proven economically viable. The price of gas is assumed to be 35 EUR / MWh, which may turn out to be wildly optimistic considering gas futures were >100 EUR / MWh over the summer 2022.

I find it concerning that the success of this approach relies on hand-waving assumptions about the viability of unproven storage technologies when nuclear is mentioned only in a footnote for one of the scenarios. It should be a major part of every scenario. Not including it is consistent with the insane policies of some European countries to decommission their nuclear plants - Germany - but seems like a missed opportunity to test the potential of nuclear energy for achieving the 24/7 goal.

This is unique to the European study whereas the US modeling includes nuclear as part of the power generation modeling. It’s a disappointing example of the negative impact of political decisions following decades of pressure from self-defeating environmental activists.

Conclusions #

It is notoriously difficult to make projections more than a few years out, but is necessary given the long lead times for deploying energy infrastructure. It’s good to see Google funding work to consider grid-wide changes rather than privately procuring clean energy for itself or relying entirely on questionable financial instruments to back its marketing. However, the shadow of misguided anti-nuclear activism is still limiting the technologies under consideration in Europe.

That said, it is encouraging that both studies (run independently, using different software) show how it is possible to reach the goals of 24/7 carbon free energy. As with clean energy generally, the greater the demand the more opportunity for the market to develop, allowing technologies to be proven, and prices to eventually fall. That this is being spearheaded by a private company is worthy of note, but it also highlights that the goals are not just limited by the limits of technology. Long term storage still needs to be proven, but nuclear needs to be seriously considered if Europe wants to develop a secure and sustainable energy grid.

  1. I’ve ignored the obvious conclusion that moving to 24/7 carbon free energy reduces carbon emissions compared to 100% renewables matching on an annual basis. ↩︎